<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            border: 3px solid #000000;
            border-radius: 10px;
            padding: 20px;
            margin: 20px;
            width: 200px;
        }

        h3 {
            margin: 10px 0 20px 0;
        }

        p {
            margin: 20px;
        }
    </style>
</head>
<body>

<div id="app">
    <div class="box">
        <h3>小黑自动售货机</h3>
        <button @click="buy(5)">可乐5元</button>
        <button @click="buy(10)">咖啡10元</button>
    </div>
    <p>银行卡余额：{{amount}}元</p>
</div>

<script src="../lib/vue.js"></script>
<script>
    const app = new Vue({
        el: '#app',
        data: {
            amount: 100
        },
        methods: {
            buy: function(fee) {
                this.amount -= fee;
            }
        }
    })
</script>
</body>
</html>